Ballistic plate.



UNITED STATES PATENT OFFICE.

SAMUEL S. WALES, MUNHALL, PENNSYLVANIA, ASSIGNOR TO CARNEGIE STEELCOMPANY,

OF PITTSBURG, PENNSYLVANIA, A CORPORATION OF NEW JERSEY.

BALLISTIC PLATE.

My invention relates to ballistic plates,

: either with or without a carburi-zed face.

The object of the invention is to provide a new alloy which will give aplate of hi her ballistic resistance than those produced by the use ofalloys and treatments now in use.

Another object of the invention is to increase the holding resistance ofthe body of the plate by preventing the destroying of the fibrouscharacter of the body through a layer between the back roper and thesuper-carburized face, whic is nowv present in face-hardened armorplate.

The alloy now commonly used in ,the manufacture of armor plates containscarbon, manganese, nickel and chromium. In protective deck plates thesame is used with the omission of the chromium. Vanadium has also beenused in commercial steels, such as tool steels, &c.; but to my knowledgevanadium has never been used with both nickel and chromium inballisticplates. I have found that these three elements when used in ballisticplates, especially in conjunction with certain heat treatment which Ihave discovered, will greatly increase the ballisticresistance of steelplates, and produce certain other advantages.

In carryin out my process for the manilfacture of eit er face-hardenedarmor pla or protective deck plate, I use an alloy containing 22,- to 5per cent. of nickel, 1 to 2 per cent. of chromium, and below 1 per cent.of vanadium. I have found the following to be best suited for thepurpose, although other elements may be added to those speci-Speciflcation of Letters Patent.

Application filed July 18, 1907.

' Patented may 18, 1909.

Serial No. 388,637.

fied, or the proportions may be varied within certain l1mits:--

Carbon 20 to .35 per cent. Manganese 25 to 35 percent. Nickel 3. 50 toft. per cent. Chromium 1. 2,5 to 1. 7 5 per cent. Vanadium 10 to 25 percent.

The steel which I employ is preferably open hearth steel and .I preferto add the nickel as a partof the charge of the furnace in av coldcondition. I referably preheat the chromium and ad it to the open hearthcharge just before tap ing. The manganese is preferably added (3.0 d inthe ladle and the vanadium is preferably added to the ladle in the formof preheated ferro-vanadium alloy. These alloys may, however, be addedin a molten form in the ladle or otherwise as desired. The properportion of carbon maybe added by re-carburizing by the usual methods.The silicon 1 contents of the steel should be low, less than .15 .percent. The sulfur should be as low as possible, preferably less than .04per cent. It is extremely important in this vanadium alloy that thephosphorus should be -ex-,

tremely low because the vanadium is found to intensify the action ofthis element. The phosphorus-should not exceed .04 per cent.

If a face-hardened plate is to be made of considerable thickness, .theingot' may be cast and preferably forged at the ordinary forgingtemperature. If it is to be re- .forged it is subjected to a heattreatment quenched with water, the duration of the water treatment beingpreferably about one ,minute per inch of thickness, the time varyingaccording to the chemical composition of the steel, being preferablysomewhat less when the carbon content is higher. If the steel is notreforged, the heating to 900 degrees 0. and the quenching willimmediately follow the forging; the plate not being allowed to becomecold in the mean time. A further toughness may be imparted to the plateif desired by repeating these steps of heating to about 900 degrees andquenching. The steel is then raised to a temperature of about 700degrees 0., and is then allowed to cool slowly, preferably in air, andmay be rough-machined. Additional toughness is imparted to the plate bya second treatment consisting of again raising the temperature of theplate to 700 degrees 0. and allowing it to cool slowly preferably in theair. The temperature reached in this second heat treatment should beslightly lower than that in the treatment immediately preceding it. Ifthe plate needs forming it is then reheated to a proper temperature andbent or straightened as desired. This temperature should preferably notexceed the temperature of the last preceding temperatune. The plate isthen finally machined and is ready for the final water hardening, whichmay be conducted in any suitable way. I refer, however, to conduct thiswater hardbning by raising the face to be hardened to a temperature of900 degrees to 950 degrees 0. This preferably is done while keeping theback of the plate at a somewhat lower temperature, although this is notessential as the difference in temperature neednot be as great as isnecessary in the ordinary standard nickel-chromium alloy now generallyemployed.

If the plate is not to be face-hardened, but is to be a protective deckplate or simi; lar plate of thickness say under three inches, then insuch case I proceed as follows Havin cast the ingot, it may be forged orrolled to the desired thickness. It is then raised to a temperature ofabout 700 neal the plate by raising it to a temperature above 450degrees 0. and below 7 00 degrees 0., depending upon the purpose forwhich the plate is to be'used; and cool the same slowly, preferably inair. The lower the temperature of the last or third heat treatment, theharder and less ductile the material will be. I

By taking theplate after the third treat ment and again raising it toabout 900 degrees 0., water-quenching it, and re-annealing it, the platemay be further toughened. By simply repeating the third heat treatment,or annealing step, the plate may be rendered more ductile.

The advanta es of my invention result from the use of the threeelements, nickel, chromium, and vanadium in an armor or ballistic plate.r

I have discovered that while nickel intensified by vanadium isdetrimental to the is considerably increased. This discovery I believeto benew, and wish to cover the same broadly no matter what heattreatments are employed, although the above heat treatments considerablenhance the value of the ballistic plates. gne of the advantagesobtained by this alloy is that where fibrous character is imparted byheat treatment, such character is much harder to destroy by subsequenttreatments than heretofore with the alloys previously used. With theordinary nickel chromium alloy this fibrous character of the plate isdestroyed by subsequent treatments involving a temperature of 775 de ees0., or above. With my improved al oy, however, it has been found thatthe fibrous character is retained throughout the body of the plate inspite of heat treatments even rising above 900 degrees 0. Anotherpeculiar action of the vanadium in this alloy is found to be that itenables theproportion of chromium to be reduced' This is of greatadvantage since a large pro-' portion of chromium is found to make thesteel extremely sensitive to "tem erature chan es and to shock. The vanaium in-- tens es the advantageous qualities produced by chromium, thusenabling a smaller amount to be used and doing away with thedisadvantages which accrue from a large amount of chromium.

Many variations may be made in the proportions of the elements of thealloy, in the heat treatments, &c., without departing from my invention.I

'jnickel below 3.75 per cent. and below one per claim 1. As a newarticle of manufacture, a balllstic'armor or vault steel plate, composedof an alloy of iron with from .20 to .35 per cent. of carbon; .25 to .35per cent. manganese; 3.5 to 4 per cent. nickel; 1.25 to 1.75 per cent.chromium, and less than one per cent. of vanadium; substantially asdescribed.

2. As a new article of manufacture, a ballistic armor, or vault steelplate containing cent. of vanadium, substantially .as described.

3. As a new article of manufacture, a bal- I listic, armor, or vaultsteel plate containing nickel, chromium below two per cent. and belowone per cent. of vanadium, substantially as described.

4. As a new article of manufacture, a ballistic armor or vault steelplate containing. two and one-half per cent. to five per-cent.

of nickel, one per cent. to two per cent. of

chromium and below one per cent. of vanadium, substantially asdescribed.

In testimony whereof, I have hereunto set my hand.

\ J OHN 'MJLLER,

H. M. 001mm.

